1. Field of the Invention
The present invention relates to cannulas. More particularly, the present invention relates to a cannula assembly for safely puncturing a blood vessel and introducing a cannula to the puncture site.
2. Description of the Related Art
Cannulas have a wide variety of applications during surgical procedures. For example, in cardiac surgery, venous and arterial cannulas are used to conduct blood between the body and bypass equipment. Cannulas are used to conduct cardioplegia solution for both antigrade and retrograde solution administration, and cannulas are also used as vents, sumps, and for chest tube fluid suction. The structure for these known cannulas generally comprises a cannula body which is circular in cross-section and has at least one lumen extending therethrough which is similarly circular in cross-section. Examples of these structures are seen in U.S. Pat. Nos. 4,639,252, 4,129,129 and 5,395,330.
A conventional method of inserting a cannula into a body includes the steps of placing a purse string suture in the wall of a blood vessel and using a blade to puncture the center of the purse string suture. The blade is then removed, and a finger is used to cover the puncture site to prevent the loss of blood. As the finger is removed from the puncture site, the cannula is simultaneously inserted therein. One problem with this method of cannula insertion is that in many instances, such as in mini-sternotomy and minimally invasive cardiac surgery where the size of the access apertures formed in the chest cavity is minimized, it may be difficult or impossible to access and cover the puncture site with a finger, thereby resulting in a loss of blood. Another problem with this method is the difficulty in controlling the depth to which the blade or needle is inserted in the blood vessel. As a result, there is a risk that the blade or needle may be inserted too far and damage or puncture the back wall of the vessel.
One attempt to address the former problem provides a cannula that may be placed over a guide wire. To insert this cannula into a blood vessel, the center of a purse string suture is punctured with the distal end of a Selginger needle having a stylet disposed therein. Once the needle is inserted, the stylet is removed, and a finger covers the distal end of the needle to minimize blood loss. Next, the finger is removed, and a guide wire is advanced through the needle and into the blood vessel. When the guide wire is situated in the blood vessel, the needle is removed, and a dilator and cannula are placed over the guide wire. The dilator and cannula are inserted in the blood vessel until the cannula is in the desired position, at which point the dilator and guide wire are removed. While this approach eliminates the need for a finger covering the puncture site and reduces blood loss at the site, there is still blood loss at the proximal end of the needle, which must be covered by a finger during insertion of the cannula. In addition, there is no regulation of the insertion depth of the needle for preventing damage to the blood vessel.